1. Field of the Disclosure
The present invention relates to a device for providing a stent for implantation into a body lumen, more particularly for compressing a balloon-expanding stent onto a balloon catheter or for compressing a self-expanding stent to be inserted into a tube catheter, and to a method for providing the stent for an implantation.
2. Related Art
By way of example, stents are used as a medical implant for treating lesions in blood vessels. In general, a stent has a multiplicity of webs that together form a tubular shape. The stent length and, as a passage, the stent lumen with a compressible diameter extend between a proximal and a distal end. The stent assumes an expanded diameter in the dilated or released state, for example for supporting the blood vessel. The stent surface can be embodied in a hydrophilic fashion to promote hemocompatibility.
A special field of application is the vessel dilation in the field of percutaneous transluminal angioplasty, also including cardiovascular intervention. Such stents are together with a catheter, which is provided specially for this, inserted into the human body through a minimal opening, e.g. by puncturing an artery in the region of the thigh, and are moved up to the lesion, i.e. the vessel restriction to be treated, and are dilated there. Whereas the stent remains in the dilated blood vessel and supports the latter from the inside, the catheter is removed from the body. The flow of blood through the dilated and supported blood vessel is once again ensured. This procedure is carried out with the aid of instantaneous X-ray recordings, which on a monitor display both the blood vessels and the instruments inserted into the body.
Another special field of application is the treatment of aneurysms, i.e. expanded blood vessels. In this treatment, a stent graft—consisting of a supporting mesh and a cover—is inserted into the aneurysm in order once again to ensure the conventional blood flow. Furthermore, a stent can also comprise further functional elements, such as closure elements for closing a lumen, valve-replacement elements, etc., as known in the prior art.
Moreover, stents in the prior art are widely used in a multiplicity of additional medical applications. A distinction is substantially made between balloon-expanding and self-expanding stents. Prior to implantation, balloon-expanding stents are applied to a non-expanded balloon. To this end, the stent is, for example, compressed to a smaller diameter over the balloon and inserted into the body together with the balloon. The balloon is expanded at the treatment site, e.g. at a lesion or a vessel valve, such that it dilates the stent. The balloon may subsequently be removed from the body. By way of example, self-expanding stents consist of a metal with memory effect. They can be compressed against their elastic force in order to be inserted into a body lumen and can be inserted into a supply catheter. They are released from the catheter at the treatment site and jump back to their expanded state.
However, the metallic stents implanted into blood vessels harbor certain risks for the patient. Inter alia, thromboses can form at the structures of the stent. Combined with medicaments administered to the patient after the implantation, the occurrences of thromboses in the case of bare metal stents (BMS) could be reduced to less than 1% within the first 10 days. Nevertheless, this is one of the most-feared complications, particularly in the case of the coronary intervention.
A property of the stent that is desired by medical practitioners is the rapid growing in thereof, the so-called reendothelialization. The latter is of the utmost importance for the success of the stent therapy because the cells in this endothelial layer form essential antithrombotic factors. However, as long as the stent has not grown in, and the structures thereof are subjected to the blood flow, it is of the utmost importance to provide an antithrombotic stent surface.
It is well-known that stents with hydrophilic surface properties have a much higher hemocompatibility, i.e. a much lower thrombogenicity. Substances are applied onto the stent surface, for example by means of coating methods, in order to increase the hydrophilicity on the stent surfaces.
By way of example, possible coating methods include “chemical vapor deposition” (CVD) or “physical vapor deposition” (PVD), by means of which materials, e.g. polymers or metals with defined layer thicknesses, are applied onto the stent surface. It was found that in the case of a polymer-coated BMS, the thrombocyte formation was reduced from 85% (BMS) to 20% (polymer-coated BMS) as a result of the increased hydrophilic properties of the surface.
The stent surface is coated with an active substance in a further application. By way of example, glucocorticoids, cytostatic agents, immunomodulators or antiproliferative agents are used as active substances. The substances, and hence the medical active ingredient, are successively released after the stent is implanted into the body.
It is common to all stents that these need to have a smaller diameter for being introduced into a body lumen than when they carry out their function in the body. In general, the producer pre-fits the stents on a catheter and packages them. However, a stent may also be compressed only just before said stent is inserted into the body lumen. In conventional methods for providing a stent for implantation, the stent is usually subjected to the necessary surface treatment in an expanded or semi-expanded state and subsequently compressed to a smaller diameter, which is suitable for the insertion into the body of a patient, by means of a crimping apparatus.
By way of example, U.S. Pat. No. 6,968,607 B2 discloses a crimping apparatus consisting of a plurality of crimping segments. The ends of the crimping segments are attached to a drum along a circle and can be pivoted about a pivot, which is at a distance from the attachment point. The other end of the crimping segments can be pivoted toward the center of the circle by rotating the drum. In the pivoted-open state, the crimping segments form a central opening therebetween, into which a stent can be inserted such that the segments encompass the stent. When the segments are pivoted toward the center of the circle, the central opening is reduced and the individual segments press against the external circumference of the stent from all sides such that the latter is compressed. The drum can be rotated by means of an actuation lever. The stents are fed to the crimping apparatus through an input and output opening and are removed in the crimped state.
Similar crimping apparatuses, for example with an integrated device for tempering the stent during the crimping process, or for example with an integrated device that provides the stent with an envelope during the compression, are known from US 2008/0072653 A1 and WO 2006/050425 A2.
In another crimping apparatus according to U.S. Pat. No. 6,141,855, a stent is encompassed by a Mylar film. The ends of the film are guided through a slit in a solid plate, and so the film forms a loop with a variable diameter, within which the stent is arranged. In order to compress the stent, the ends of the film are pulled such that the diameter of the loop is reduced and the stent is pressed together by the film. By way of example, this crimping apparatus can be used to crimp the stent onto e.g. the balloon of a balloon catheter.
When a stent for implantation is provided using crimping apparatuses from the prior art, the stents are generally subjected to the surrounding environment in an unprotected fashion during the insertion into the crimping apparatus and are contacted by the elements of the crimping apparatus. In the process, they are subjected to contamination by e.g. reagents situated in the air, such as hydrocarbon molecules, which can adversely affect a hydrophilic surface of a stent or an active substance on the stent. The stent surface can also be contaminated by residues on the elements of the crimping apparatus. Furthermore, there is the risk of undesired contamination of or change in the stent surface when transferring a crimped stent from a conventional crimping apparatus.